Melissa R. Wuellner (Melissa is a PhD student working under Dr. David Willis)
South Dakota State University
We continue to examine competition between walleye and smallmouth bass using basic approaches. Anecdotal evidence suggests that smallmouth bass may displace walleye from rocky littoral habitats, thus forcing walleye to pelagic habitats. In July 2008, we will begin a series of experiments that examines competition for limited habitat between walleye and smallmouth bass. We will record habitat use and any agonistic behaviors that fish may display in defending their habitat.
We will also examine competition for food between age-1 walleye and smallmouth bass this summer. Previous experiments showed that smallmouth bass may be the better competitor (as indexed by growth) of the two species. However, fish were fed during daytime hours. In the next round of experiments, we will feed fish during a period encompassing dusk, thus testing the effects of light level on food competition between walleye and smallmouth bass.
Finally, we are currently running experiments examining ontogenetic diet shifts of age-0 smallmouth bass. We are examining growth rates and prey selectivity of four size categories (20, 40, 60, and 80 mm) of bass on three diets (zooplankton, amphipods, and larval fathead minnows). We hope to present the results of these experiments during the upcoming 2008 Midwest Fish and Wildlife Conference.
The Natural Reproductive Cycle of Northern Largemouth Bass Micropterus salmoides salmoides in the Upper Midwest, with Applications to Out-of-season Production
Dan Spengler (M.S. student, advised by Dr. Mike Brown)
The objective of this project is to characterize the natural reproductive cycle in male and female northern largemouth bass. Largemouth bass (five male and five female) have been collected monthly for one year (August through July 2008) from a private impoundment located approximately 9.5 miles northeast of Brookings, SD. Blood from each bass was collected from the caudal vein and later centrifuged at 1000 x g to obtain plasma. All plasma samples will be assayed using radio-immunoassay procedures to determine seasonal fluctuations among plasma sex steroid hormones 11-ketotestosterone, testosterone, and estradiol-17β. Seasonal fluctuations of the egg yolk precursor protein, vitellogenin, will also be evaluated in females with ELISA analysis. These assays will commence on 20 July. Following blood procedures, all fish were necropsied to determine the following organosomatic indices: gonadosomatic, hepatosomatic, and visceral somatic indices, in addition to a mesenteric fat ranking. Six gonads (three ovaries and three testes) were also taken from each monthly sample for histological processing. These histological slides will allow us to determine ovarian and testicular maturity over a temporal regime. In addition to these physiological parameters, key physical effects known to influence reproductive behavior (e.g. photoperiod and temperature) were monitored in situ using data loggers during the cycle. Results from this study should be completed by fall 2008 and this information will ultimately be applied to out-of-season spawning procedures for northern largemouth bass, commencing this fall.
Evaluating smallmouth bass seasonal sampling dynamics and diets
Tom Bacula (M.S. student advised by Dr. David Willis and Dr. Brian Blackwell)
This project is over half way competed with a few more monthly electrofishing and modified-fyke net samplings to occur this year. The preliminary results from Enemy Swim and Roy lake (completed in 2007) show that sampling in May resulted in the capture of a broad size distribution of individuals using nighttime boat electrofishing. In the fall there was higher catch per unit effort using electrofishing, however the collection was dominated by fish shorter than stock length fish (180 mm). The diet analysis was variable by size of individual and season, while small fish (less than 280 mm) consumed invertebrates in the spring and switched to fish in the summer and fall. The larger fish consumed primarily crayfish across all seasons. The results are preliminary with completion in the Spring of 2009.